Unless otherwise indicated herein, the description provided in this section is not prior art to the claims and is not admitted to be prior art by inclusion in this section.
To provide cellular wireless communication service, a wireless carrier typically operates a radio access network (RAN) that includes a number of base stations that radiate to define wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) (also known as wireless communication devices (WCDs)) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly-equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the RAN may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
In general, a RAN may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handoff between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or blocks of frequencies (e.g., frequency bands, such as 698-960 MHz, 1610-2025 MHz, etc.) and may define a number of air interface channels for carrying information between the base station and UEs. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing, for instance. By way of example, each coverage area may define a pilot channel, reference channel, or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that UEs may detect as an indication of coverage and may measure to evaluate coverage strength. As another example, each coverage area may define one or more uplink control channels or other resources on which UEs may transmit control messages to the base station. And each coverage area may define one or more downlink control channels or other resources on which the base station may transmit control messages or other information to UEs. Further, each coverage area may define one or more traffic channels or other resources for carrying bearer communication traffic such (e.g., user traffic or application level traffic) as voice data and other data between the base station and UEs.
When a UE first powers on or enters into coverage of the RAN, the UE may scan for and identify a strongest pilot or reference signal and may register with the RAN by transmitting a registration request or attach request to a base station providing that signal. This registration process may serve to notify the RAN of the UE's presence in a particular coverage area and to facilitate network authentication of the UE. Once registered, the UE may then operate in an idle mode in which the UE monitors a downlink control channel to receive overhead information and to check for any page messages. In the idle mode, the UE may have no assigned traffic channel resources on which to engage in bearer communication.
When the RAN has a communication (such as a voice call or other traffic) to provide to a UE that is registered with the RAN but is operating in the idle mode, the RAN may page the UE in an effort to then facilitate assigning traffic channel resources to the UE. In particular, the RAN may transmit on the downlink a page message addressed to the UE. Assuming the UE receives this page message, the UE may then transmit to the RAN a page response message on the uplink. And upon receipt of the page response message, the RAN may then assign traffic channel resources to the UE, for use to carry the communication, thus transitioning the UE to a connected or active mode in which the UE can engage in the communication.
Likewise, when an idle UE seeks to initiate a communication (such as to place a voice call or engage in other bearer communication), the UE may transmit on the uplink to the base station an origination or connection request, and the RAN may then assign traffic channel resources to the UE for use to carry the communication, similarly transitioning the UE to a connected or active mode in which the UE can engage in the communication.
In communication systems that provide service under more than one air interface protocol, wireless carriers may implement functionality that allows UEs to operate by default on one air interface protocol and to dynamically switch over to operate on another air interface protocol when necessary to engage in certain communications. By way of example, in a system that supports both LTE service for mobile broadband and an older protocol such as CDMA or GSM for traditional voice calls, wireless carriers may implement “circuit-switched fallback” (CSFB) functionality, which allows UEs to operate by default on LTE and to switch over to operate on the older protocol to engage in voice calls.
Under CSFB, for instance, a hybrid CDMA/LTE UE may be arranged by default to scan for and register with an LTE RAN and to operate with its CDMA radio powered off, but to then engage in control signaling with the CDMA RAN via the LTE RAN, i.e., over the LTE air interface. To facilitate this, when the UE registers with the LTE RAN, the UE may also transmit to an interworking server (IWS), via the LTE RAN infrastructure (e.g., a mobility management entity (MME)), a registration request message, which the IWS may then send to the CDMA RAN to facilitate registration of the UE with the CDMA RAN. Further, an LTE base station of the LTE RAN may regularly broadcast a System Information Block #8 (SIB8) message containing data that indicates to a UE considering registering to be served by the LTE base station whether CSFB service is currently supported by the LTE base station.
When the CDMA RAN has a voice call to connect to the UE, the CDMA RAN may signal through the IWS to the LTE RAN to cause the LTE RAN to transmit a CSFB page message to the UE over the LTE air interface. After further CSFB signaling through the LTE RAN, the UE may then power on its CDMA radio and tune to the CDMA RAN to engage in the call over the CDMA air interface.
In one implementation of this CSFB process, for instance, once the UE receives the CSFB page message for the incoming CSFB call, the UE may transmit a CSFB extended service request message to its serving LTE base station as a request to set up the incoming CSFB call. In turn, the LTE base station may then send to the UE a list of CDMA coverage areas on which the CDMA RAN provides service, possibly specifying for each such coverage area its operating carrier and coverage area identifier (e.g., PN offset or physical cell identifier), so as to enable the UE to scan for coverage of the CDMA RAN as part of the CSFB process. Such a list may be referred to herein as a “CSFB scan-list” or simply a “scan-list.” In some scenarios, after the UE sends the CSFB extended service request message to the LTE base station, the LTE base station may in turn send to the UE a control message that includes the scan-list. The control message may, upon receipt by the UE, trigger the UE to use the scan-list to scan for CDMA coverage.
Alternatively, in other scenarios, the SIB8 message broadcast by the LTE base station may include the scan-list, and/or may otherwise include information about the local CDMA RAN that the UE may interpret to determine one or more CDMA base stations of which the UE can scan for coverage. The SIB8 message can be received by the UE either before or after the UE sends the CSFB extended service request message, which may depend on how often the SIB8 message is broadcast. The UE may then scan for CDMA coverage in accordance with the scan-list included as part of the regularly-broadcast SIB8 message.
Furthermore, the UE may use its CDMA radio to scan for coverage of each of the listed coverage areas and transmit to the LTE base station a report of the strongest CDMA pilot signals and corresponding signal strengths that the UE detected. The LTE RAN may then pass those pilot signal measurements via the IWS to the CDMA RAN, and the CDMA RAN may use those measurements as a basis to determine a CDMA coverage area and traffic channel to assign to the UE. The CDMA RAN may then transmit a handover direction message via the IWS to the LTE RAN, which the LTE RAN may transmit to the UE, directing the UE to transition to CDMA to communicate in the assigned CDMA coverage area on the assigned traffic channel. The UE may then use its CDMA radio to tune to the assigned channel and to engage in the call via CDMA.
Likewise, when the UE is served by the LTE RAN and has a voice call to place, the UE may transmit over the LTE air interface to its serving LTE base station a CSFB extended service request message to request setup of an outgoing CSFB call, and the LTE base station may similarly send to the UE a scan-list of CDMA coverage areas on which the local CDMA RAN provides service. The UE may then similarly tune to CDMA and scan for coverage of each of the listed CDMA carriers, and report the strongest detected CDMA pilots to the LTE base station. And the CDMA RAN may similarly determine a CDMA coverage area and traffic channel to assign to the UE and transmit a handover direction message via the IWS to the LTE RAN for transmission to the UE. The UE may then similarly use its CDMA radio to tune to the assigned channel and to engage in the call via CDMA. This CSFB call setup process is generally quite efficient, as it allows the UE to engage in CDMA voice call setup through its existing LTE connection, without the need for the UE to be idling in CDMA coverage in the first place.
In an alternate CSFB process, after the UE sends a CSFB extended service request message as noted above, the UE's serving LTE base station may transmit to the UE a “release-and-redirect” message, which directs the UE to leave the LTE RAN and search for, find, and acquire connectivity in the CDMA RAN. To facilitate the UE searching for CDMA coverage, the LTE base station may also send to the UE a scan-list specifying CDMA coverage areas on which the local CDMA RAN provides service. In line with the discussion above, the SIB8 message broadcast by the LTE base station may include the scan-list, or the LTE base station may send to the UE a control message that includes the scan-list. In scenarios where the LTE base station sends the control message, the control message may be included as part of the release-and-redirect message or may be sent as a separate message. Once the UE has registered with the CDMA RAN, the CDMA RAN may then connect the CSFB call for the UE.
Generally, a wireless carrier may implement many “macro” base stations throughout its RAN, to provide UEs served by those base stations with widespread cellular coverage. In recent years, however, the cellular wireless industry has begun to expand beyond traditional macro base stations, by now providing users and companies with private base stations commonly known as “femtocells” (but also known by other names, such as microcells, femtocell base stations, and private base stations, among others). A typical femtocell may be a small device, about the size of a WiFi access point, which may connect with a broadband wireless connection to the Internet and establish a virtual private network (VPN) connection via the Internet with the wireless carrier's core network (e.g., with a femtocell controller on the wireless carrier's RAN). The femtocell may radiate to define a wireless coverage area in much the same way as a macro base station does. The femtocell uses the broadband Internet connection to connect with the wireless carrier's RAN and to provide much of the same functionality as a macro base station. A femtocell may provide service on a single carrier frequency (or on a single carrier frequency per technology, where multiple technologies are supported), and also transmit administrative messages and parameters that UEs can use to connect with the femtocell.
Femtocells serve the beneficial purpose of allowing subscribers to improve cellular coverage, perhaps in locations where the macro RAN does not provide adequate coverage. As such, individuals and companies may acquire femtocells from the wireless carrier and may position the femtocells at desired locations, such as within a house or throughout a corporate campus.
To help control where the wireless carrier provides service, the wireless carrier may require femtocells that access its RAN to register their geographic location with the wireless carrier, and the wireless carrier may authenticate and authorize the femtocells for use in the reported locations. For instance, when an individual subscriber acquires a femtocell from the wireless carrier for use in the in the subscriber's house, the wireless carrier may record in a profile record for the subscriber an indication of the geographic coordinates of the subscriber's home. When the subscriber powers up the femtocell, the femtocell may then determine its geographic location, or “geolocation,” through use of a Global Positioning System (GPS) receiver for instance, and may transmit the geolocation via its broadband connection to the wireless carrier's RAN. The RAN may then verify that the reported geolocation matches the geolocation recorded in the subscriber's profile record and, only if so, may authorize the femtocell to operate as a base station for the wireless carrier's RAN. From time to time during operation, the femtocell may then again report its geolocation to the wireless carrier's RAN, and the wireless carrier may condition continued operation of the femtocell on the reported geolocation being valid.